The invention relates to an optical focussing device, for focussing a radiation beam emanating from a radiation source onto a record carrier, in particular for focussing a light beam emanating from a light source onto the reflecting surface of an information disc, comprising a frame; an objective having a free end to be directed to the record carrier and having an optical lens system accommodated in a lens mount; a drive system for axially moving the objective relative to the frame in the direction of its optical axis; as well as axial guide means for axially guiding the objective relative to the frame.
Such an optical focussing device is for example known from the Applicant's U.S. Pat. No. 4,021,101. The optical focussing device described in said Patent is intended to focus a light beam from a helium-neon laser onto an optically readable video disc. The objective is movable in the direction of its optical axis over a distance which is limited by stops. This distance is sufficiently large to ensure that in any situation occurring during use the objective is capable of focussing the light beam on the information surface of the video disc in the required manner. In such optical focussing devices contact between the objective and the information disc may be inevitable under certain circumstances. In the previously mentioned video disc players the objective for example is disposed at a distance of only approximately 2 mm from the video disc surface during operation. Under unfavourable circumstances, for example in the event of a fault in the focussing control circuit during operation or when it is attempted to play a video disc which has been deformed to such an extent that the disc no longer meets the specifications imposed on video discs in respect of disc flatness, the objective may touch the disc surface. Such contact between the objective and the video disc may give rise to damaging of the objective as well as of the disc surface. In the latter case this may result in video information which can no longer be read satisfactorily at the damaged location.